The chemical syntheses of 2'(3')-theta-aminoacyl, 2'(3')-theta-(N- acylaminoacyl) and 2'(3')-theta-peptidyl oligoribonucleotides having different chain lengths, base sequences and amino acids will be undertaken, and these compounds will be used to study the substrate specificity of ribosomal peptidyl transferase at the A and P sites. The biochemical studies will be carried out using several ribosomal transfer and binding systems. The substrate specificity of certain antibiotics that inhibit protein biosynthesis will also be investigated.